1. Field Of The Invention
This invention relates to an improved roof support for an underground mine or the like, and more specifically to a roof support which utilizes a horizontal cross member to provide tension between a pair of roof anchors that are fixed into bore holes formed in the roof.
2. Description Of The Prior Art
Numerous methods and structures have been provided for supporting the roof of mines or other underground passages. One type of structure, which is commonly employed, includes a roof truss which generally provides two inclined cords and a horizontal cord. The inclined cords are usually mine roof bolts or roof anchors which extend into holes in the mine roof at about a 45.degree. angle to the vertical. The mine roof bolts may be anchored in the inclined holes in the roof by well known means such as mechanical expansion shells, resin bonding, or a combination of mechanical expansion shells and resin bonding. The horizontal cord or cross member extends across the mine roof between the roof anchors. The horizontal cord applies tension between the roof anchors to generate an upward force on the roof and provided stability to the roof.
U.S. Pat. No. 2,667,037 discloses a general roof support system which provides the type of upward forces described above. Specifically, a horizontal beam is positioned transversely of the mine opening across the roof and is retained in placed by a plurality of inclined bolts which anchor the horizontal beam and provide over-all integrity for the roof support.
U.S. Pat. No. 3,427,811 discloses a system which provides the same type of upward forces to support a mine roof but includes the additional features of a means for varying the tension on the horizontal cord or cross member. U.S. Pat. No. 3,505,824 and U.S. Pat. No. 3,509,726 disclose roof support trusses similar to U.S. Pat. No. 3,427,811 but which employ different elements to create a combined tension on the inclined cord and the horizontal cord components.
U.S. Pat. No. 4,395,161 describes a roof plate utilized in the truss type systems described above. U.S. Pat. No. 4,601,616, assigned to the assignee herein, discloses a roof support of the type generally described above which includes a tool for tensioning the cross member or horizontal cord.
U.S. Pat. No. 3,455,200 discloses a roof anchor that has an eyelet on the outer end. The eyelet is utilized to retain a cross piece that holds wire mesh screening in place to cover the roof and walls of a mine passage.